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What is the coefficient of x² in the expansion of (1 + x)⁵ * (1 + 2x)⁴?
- 74
- 88
- 96
- 108
Correct answer: 74
Solution
Picking terms from (1+x)⁵ and (1+2x)⁴ that multiply to give x²: (1)(6*4*x²) + (5x)(4*2x) + (10x²)(1) = 24 + 40 + 10 = 74.
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